The objective of the study was to investigate the effect of linseed and rapeseed or respective oils on performance indices, nutrient digestibility, metabolizable energy of diets, digesta viscosity, and yield and chemical composition of edible and non-edible parts of the carcass of broiler chickens, with particular attention to n-3 PUFA. Two experiments were performed on 134 female broiler chickens, randomly allocated to 3 groups of 22 birds (Experiment 1) or 2 groups of 24 birds (Experiment 2) and 10 birds to a zero group. The chickens were kept in individual cages. Five wheat-based and xylanase-supplemented diets containing about 80 g crude fat per kg were prepared. The source of added fat was in control diet lard (61 g/kg), in experimental diets half of the lard was substituted by: linseed oil (LO) or full-fat linseed (L), rapeseed oil (RO) or full-fat rapeseed (R). Chickens were given the control or experimental diets from days 8 to 42 of life, then they were slaughtered, the carcasses were divided into edible and non-edible parts, and their chemical composition determined. Feeding diet with rapeseed did not significantly affect BWG or FCR, while linseed caused an increase in feed intake and subsequent deterioration in FCR, which in groups C, LO, and L equalled 1.82, 1.73 and 2.0, respectively. The viscosity of jejunal digesta in group L reached 4.5 mPas.s in comparison with about 1.5 in all of the remaining groups. Organic matter retention and AME_N value of diet L was lower than in diets C and LO (P≤0.05), while apparent protein and fat digestibility, organic matter retention, and the AME_N value of diet R was lower than RO (P≤0.01). Protein retention and meat yield was lower in group L than in both of the other groups (P≤0.05). The deposition of n-3 PUFA in the carcass was in groups R and RO 2 times greater, in groups L and LO 8 times greater than in the control group. The ratio of n-6/n-3 PUFA, which approximated 10 in edible parts of broilers from the control group, decreased to about 4.7 in groups R and RO, and to about 1.3 in groups L and LO. This shift may be considered favourable for consumers of broiler meat, as an increase of n-3 fatty acid intake is connected with health benefits in humans.